arXiv subjects

Andrea Donini

Publications and source records attributed to Andrea Donini.

At least 19 recordsLinked to original sources

arXiv2026

Inflation in Extra-Dimensions with one or two branes

In this paper, we study two inflationary models, namely, monomial inflation and the simplest $\alpha$-attractor inflation, within extra-dimensional frameworks. We consider three extra-dimensional setups: Dark Dimension, which embeds one flat extra-dimension to explain the observed smallness of the 4D cosmological constant $\Lambda_4$; and the two Randall-Sundrum scenarios with one warped extra-dimension, namely RS1 with two branes and RS2 with one brane. We derive the corresponding Friedmann equations, compute the slow-roll parameters in each case, and we fit the experimental data for ($n_s - 1$, $\alpha$, $\Delta_s^2$, $r$), using Planck, BICEP, and ACT data. We find that monomial inflation is strongly disfavored in all scenarios, while $\alpha$-attractor inflation provides an excellent fit to current observations, with extra-dimensional setups offering additional flexibility compared to the standard 4D case.

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arXiv2025

Leading large $N_c$ contributions to Lepton Number Violating Meson Decays

Lepton number violating meson decays, such as $M_1^- \to M_2^+\ell_1^-\ell_2^-$, provide constraints on $d=9$ $ΔL = 2$ operators. RGE-improved bounds on the Wilson coefficients of these operators have been presented in the literature, taking into account perturbative QCD one-loop corrections and the corresponding operator mixing. Here, we present for the first time the contribution of connected diagrams to the hadronic matrix elements $\langle M_2 | {\cal O}_h | M_1 \rangle$. These diagrams, usually overlooked under the assumption that $\langle M_2 | {\cal O}_h | M_1 \rangle \sim \langle M_2 | J_{q_3 q_4} | 0 \rangle \times \langle 0 |J_{q_1 q_2} | M_1 \rangle \gg \langle M_2 | J_{q_3 q_2} \times J_{q_1 q_4} | M_1 \rangle$, can give indeed a significant contribution to the matrix element. Including these connected diagrams is but the first step towards a full non-perturbative computation of the long-range QCD effects in these operators, that should be performed using lattice field theory techniques. However, connected diagrams represent the leading order in the $1/N_c$ expansion of the QCD non-perturbative effects and thus our work can be understood as a realistic, first approximation to a complete calculation of the long-range part of the matrix elements.

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arXiv2025

Dark Matter in a Three-Brane Randall-Sundrum Scenario out of the Evanescent Limit

The Nature of Dark Matter (DM), that constitutes approximately 25\% of the energy density in the Universe, is still eluding us. An intriguing possibility is that DM does indeed interacts with SM particles only gravitationally (the only mean by which we have detected it so far), albeit in an extra-dimensional scenario yet it has not been possible to detect it by some non-gravitational means. In a three-brane Randall-Sundrum setup, with DM located on a Deep Infra-Red GeV-TeV brane, and the SM on an Infra-Red TeV-PeV one, it was shown to be possible to recover the observed DM relic abundance and somewhat relax the hierarchy problem, whilst avoiding LHC stringent bounds on DM and KK graviton masses that constrain severely similar two-brane setups. The phenomenological results, however, have been obtained under the assumption that the bulk curvatures on the left ($k_1$) and the right ($k_2$) of the intermediate IR-brane are identical, $k_2 \to k_1$. Since the brane tension $\sigma_{\rm IR}$ of the intermediate brane is proportional to $k_2 - k_1$ and, therefore, vanishes, it is clear that this limit (for which the IR-brane becomes {\em evanescent}) is unphysical. We could say that this is {\em no brane}: if the brane tension of a brane vanishes, there is no brane in the bulk (pun intended). In this paper, therefore, we study in detail the theoretical framework needed to explore this interesting phenomenological possibility, {\em out of the evanescent brane limit}. We show that most of the formul\ae $\,$used in the {\em evanescent limit} are still valid for ${\cal O}(1)$ differences between $k_1$ and $k_2$ (thus, introducing no new unjustified hierarchy in the bulk). Once the relevant couplings of radions and KK gravitons are computed, we study the (enlarged) parameter space of the model looking for the region in which the relic DM abundance is recovered.

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arXiv2025

Dark Matter in an Evanescent Three-Brane Randall-Sundrum Scenario

Apart from its gravitational interactions, dark matter (DM) has remained so far elusive in laboratory searches. One possible explanation is that the relevant interactions to explain its relic abundance are mainly gravitational. In this work we consider an extradimensional Randall-Sundrum scenario with a TeV-PeV IR brane, where the Standard Model is located, and a GeV-TeV deep IR (DIR) one, where the DM lies. When the curvatures of the bulk to the left and right of the IR brane are very similar, the tension of the IR brane is significantly smaller than that of the other two branes, and therefore we term it \evanescent". In this setup, the relic abundance of DM arises from the freezeout mechanism, thanks to DM annihilations into radions and gravitons. Focusing on a scalar singlet DM candidate, we compute and apply current and future constraints from direct, indirect and collider-based searches. Our findings demonstrate the viability of this scenario and highlight its potential testability in upcoming experiments. We also discuss the possibility of inferring the number of branes if the radion and several Kaluza-Klein graviton resonances are detected at a future collider.

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arXiv2023

Towards a realistic setup for a dynamical measurement of deviations from Newton's $1/r^2$ law: the impact of air viscosity

A novel experimental setup to measure deviations from the $1/r^2$ distance dependence of Newtonian gravity was proposed in arXiv:1609.05654. The underlying theoretical idea was to study the orbits of a microscopically-sized planetary system composed of a ``Satellite'', with mass $m_{\rm S} \sim {\cal O}(10^{-9})$ g, and a ``Planet'', with mass $M_{\rm P} \sim {\cal O} (10^{-5}) $ g at an initial distance of hundreds of microns. The detection of precession of the orbit in this system would be an unambiguous indication of a central potential with terms that scale with the distance differently from $1/r$. This is a huge advantage with respect to the measurement of the absolute strength of the attraction between two bodies, as most electrically-induced background potentials do indeed scale as $1/r$. Detection of orbit precession is unaffected by these effects, allowing for better sensitivities. In arXiv:2106.08611, the impact of other subleading backgrounds that may induce orbit precession, such as, {\em e.g.}, the electrical Casimir force or general relativity, was studied in detail. It was found that the proposed setup could test Yukawa-like corrections, $α\times \exp(-r/λ)$, to the $1/r$ potential with couplings as low as $α\sim 10^{-2}$ for distances as small as $λ\sim 10$ $μ$m, improving by roughly an order of magnitude present bounds. In this paper, we start to move from a theoretical study of the proposal to a more realistic implementation of the experimental setup. As a first step, we study the impact of air viscosity on the proposed setup and see how the setup should be modified in order to preserve the theoretical sensitivity achieved in our previous works.

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arXiv2022

Generalising Holographic Superconductors

In this paper we propose a generalised holographic framework to describe superconductors. We first unify the description of s-, p- and d-wave superconductors in a way that can be easily promoted to higher spin. Using a semi-analytical procedure to compute the superconductor properties, we are able to further generalise the geometric description of the hologram beyond the AdS-Schwarzschild Black Hole paradigm, and propose a set of higher-dimensional metrics which exhibit the same universal behaviour. We then study the properties of the condensate and the scaling of the critical temperature with the parameters of the higher-dimensional theory, reproducing existing results in the literature and extending them to include a possible description of the newly observed f-wave superconducting systems.

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arXiv2021

Spin-dependence of Gravity-mediated Dark Matter in Warped Extra-Dimensions

We study the spin-dependence of Dark Matter (DM) particles which interact gravitationally with the Standard Model (SM) in an extra-dimensional Randall-Sundrum scenario. We assume that both the Dark Matter and the Standard Model are confined to the TeV (Infra-red) brane and only interact via gravitational mediators, namely Kaluza-Klein gravitons and the radion. We analyze the different DM annihilation channels and find that it is possible to achieve the presently observed relic abundance of Dark Matter, $Ω_{\rm DM}$, within the freeze-out mechanism for DM particles of spin 0, 1/2 and 1. We study the region of the model parameter space for which $Ω_{\rm DM}$ is achieved and compare it with the different experimental and theoretical bounds. We also consider the impact of the radion in the phenomenology. We find that, for DM particles mass $m_{\rm DM} \in [1,15]$ TeV, most of the parameter space is excluded by the current constraints or will be excluded by the LHC Run III or by the LHC upgrade, the HL-LHC. The presence of the radion does not modify significantly the non-excluded region. The observed DM relic abundance can still be achieved for DM masses $m_{\rm } \in [4,15]$ TeV and $m_{G_1} < 10$ TeV for scalar and vector boson Dark Matter. On the other hand, for spin 1/2 fermion Dark Matter, only a tiny region with $m_{\rm DM } \in [4, 15]$ TeV, $m_{G_1} \in [5,10]$ TeV and $Λ> m_{G_1}$ is compatible with theoretical and experimental bounds.

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arXiv2021

FIMP Dark Matter in Clockwork/Linear Dilaton Extra-Dimensions

We study the possibility that Dark Matter (DM) is made of Feebly Interacting Massive Particles (FIMP) interacting just gravitationally with the Standard Model particles in the framework of a Clockwork/Linear Dilaton (CW/LD) model. We restrict here to the case in which the DM particles are scalar fields. This paper extends our previous study of FIMP's in Randall-Sundrum (RS) warped extra-dimensions. As it was the case in the RS scenario, also in the CW/LD model we find a significant region of the parameter space in which the observed DM relic abundance can be reproduced with scalar DM mass in the MeV range, with a reheating temperature varying from 10 GeV to $10^{9}$ GeV. We comment on the similarities of the results in both extra-dimensional models.

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arXiv2020

Kaluza-Klein FIMP Dark Matter in Warped Extra-Dimensions

We study for the first time the case in which Dark Matter (DM) is made of Feebly Interacting Massive Particles (FIMP) interacting just gravitationally with the standard model particles in an extra-dimensional Randall-Sundrum scenario. We assume that both the dark matter and the standard model are localized in the IR-brane and only interact via gravitational mediators, namely the graviton, the Kaluza-Klein gravitons and the radion. We found that in the early Universe DM could be generated via two main processes: the direct freeze-in and the sequential freeze-in. The regions where the observed DM relic abundance is produced are largely compatible with cosmological and collider bounds.

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arXiv2020

Dissecting the $ΔI= 1/2$ rule at large $N_c$

We study the scaling of kaon decay amplitudes with the number of colours, $N_c$, in a theory with four degenerate flavours, $N_f=4$. In this scenario, two current-current operators, $Q^\pm$, mediate $ΔS=1$ transitions, such as the two isospin amplitudes of non-leptonic kaon decays for $K\to (ππ)_{I=0,2}$, $A_0$ and $A_2$. In particular, we concentrate on the simpler $K\toπ$ amplitudes, $A^\pm$, mediated by these two operators. A diagrammatic analysis of the large-$N_c$ scaling of these observables is presented, which demonstrates the anticorrelation of the leading ${\mathcal O}(1/N_c)$ and ${\mathcal O}(N_f/N_c^2)$ corrections in both amplitudes. Using our new $N_f=4$ and previous quenched data, we confirm this expectation and show that these corrections are $naturally$ large and may be at the origin of the $ΔI=1/2$ rule. The evidence for the latter is indirect, based on the matching of the amplitudes to their prediction in Chiral Perturbation Theory, from which the LO low-energy couplings of the chiral weak Hamiltonian, $g^\pm$, can be determined. A NLO estimate of the $K \to (ππ)_{I=0,2}$ isospin amplitudes can then be derived, which is in good agreement with the experimental value.

hep-lat↗

arXiv2020

Gravity-mediated Dark Matter in Clockwork/Linear Dilaton Extra-Dimensions

We study for the first time the possibility that Dark Matter (represented by particles with spin $0,1/2$ or $1$) interacts gravitationally with Standard Model particles in an extra-dimensional Clockwork/Linear Dilaton model. We assume that both, the Dark Matter and the Standard Model, are localized in the IR-brane and only interact via gravitational mediators, namely the Kaluza-Klein (KK) graviton and the radion/KK-dilaton modes. We analyse in detail the Dark Matter annihilation channel into Standard Model particles and into two on-shell Kaluza-Klein towers (either two KK-gravitons, or two radion/KK-dilatons, or one of each), finding that it is possible to obtain the observed relic abundance via thermal freeze-out for Dark Matter masses in the range $m_{\rm DM} \in [1, 15]$ TeV for a 5-dimensional gravitational scale $M_5$ ranging from 5 to a few hundreds of TeV, even after taking into account the bounds from LHC Run II and irrespectively of the DM particle spin.

hep-ph↗

arXiv2020

Gravity-mediated Scalar Dark Matter in Warped Extra-Dimensions

We revisit the case of scalar dark matter interacting just gravitationally with the Standard Model (SM) particles in an extra-dimensional Randall-Sundrum scenario. We assume that both, the dark matter and the Standard Model, are localized in the TeV brane and only interact via gravitational mediators, namely the graviton Kaluza-Klein modes and the radion. We analyze in detail the dark matter annihilation channel into two on-shell KK-gravitons, and contrary to previous studies which overlooked this process, we find that it is possible to obtain the correct relic abundance for dark matter masses in the range [1, 10] TeV even after taking into account the strong bounds from LHC Run II. We also consider the impact of the radion contribution (virtual exchange leading to SM final states as well as on-shell production), which does not significantly change our results. Quite interestingly, a sizeable part of the currently allowed parameter space could be tested by LHC Run III and by the High-Luminosity LHC.

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arXiv2019

Meson interactions at large $N_c$ from Lattice QCD

We report on the computation of the scaling of QCD observables with the number of colours, $N_c$. For this, we use dynamical configurations with four active flavours, $N_f=4$, and values of $N_c=3-6$. We study the meson masses and decay constants, and compute the leading and subleading contributions to the Low Energy Constants (LECs) of the chiral Lagrangian. We also explore $ππ$ scattering in the $I=2$ channel, and compute the $K \to π$ weak decay matrix elements. We comment on the relation of the latter to $K \to ππ$ processes and the $ΔI=1/2$ rule.

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arXiv2018

Follow-up on non-leptonic kaon decays at large $N_c$

We report on the status of our dynamical simulations of a $SU (N_c )$ gauge theory with $N_c=3-6$ and $N_f =4$ fundamental fermions. These ensembles can be used to study the Large $N_c$ scaling of weak matrix elements in the GIM limit $m_c=m_u$, that might shed some light on the origin of the $ΔI=1/2$ rule. We present preliminary results for the $K \to π$ matrix elements in the $N_c=3$ dynamical simulations, where we observe a significant effect of the quark loops that goes in the direction of enhancing the ratio of $A_0/A_2$ amplitudes. Finally, we present the relevant NLO Chiral Perturbation Theory predictions for the relation between $K \to π$ and $K \to ππ$ amplitudes in the light charm limit.

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arXiv2018

Neutrino tomography of the Earth

Cosmic-ray interactions with the nuclei of the Earth's atmosphere produce a flux of neutrinos in all directions with energies extending above the TeV scale. However, the Earth is not a fully transparent medium for neutrinos with energies above a few TeV. At these energies, the charged-current neutrino-nucleon cross section is large enough so that the neutrino mean-free path in a medium with the Earth's density is comparable to the Earth's diameter. Therefore, when neutrinos of these energies cross the Earth, there is a non-negligible probability for them to be absorbed. Since this effect depends on the distance traveled by neutrinos and on their energy, studying the zenith and energy distributions of TeV atmospheric neutrinos passing through the Earth offers an opportunity to infer the Earth's density profile. Here we perform an Earth tomography with neutrinos using actual data, the publicly available one-year through-going muon sample of the atmospheric neutrino data of the IceCube neutrino telescope. We are able to determine the mass of the Earth, its moment of inertia, the mass of the Earth's core and to establish the core is denser than the mantle, using weak interactions only, in a way completely independent from gravitational measurements. Our results confirm that this can be achieved with current neutrino detectors. This method to study the Earth's internal structure, complementary to the traditional one from geophysics based on seismological data, is starting to provide useful information and it could become competitive as soon as more statistics is available thanks to the current and larger future neutrino detectors.

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arXiv2017

Non-leptonic kaon decays at large $N_c$

We study the scaling with the number of colors $N_c$ of the weak amplitudes mediating kaon mixing and decay, in the limit of light charm masses ($m_u=m_d=m_s=m_c$). The amplitudes are extracted directly on the lattice for $N_c = 3-7$ (with preliminar results for $N_c = 8$ and $17$) using twisted mass QCD. It is shown that the (sub-leading) $1/N_c$ corrections to $\hat B_K$ are small and that the naive $N_c \to \infty$ limit, $\hat B_K = 3/4$, seems to be recovered. On the other hand, the ${\cal O}\, (1/N_c)$ corrections in $K \to ππ$ amplitudes (derived from $K \to π$ matrix elements) are large and fully anti-correlated in the $I=0$ and $I=2$ channels. This may have some implications for the understanding of the $ΔI=1/2$ rule.

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arXiv2013

Gain fractions of future neutrino oscillation facilities over T2K and NOvA

We evaluate the probability of future neutrino oscillation facilities to discover leptonic CP violation and/or measure the neutrino mass hierarchy. We study how this probability is affected by positive or negative hints for these observables to be found at T2K and NOvA. We consider the following facilities: LBNE; T2HK; and the 10 GeV Neutrino Factory (NF10), and show how their discovery probabilities change with the running time of T2K and NOvA conditioned to their results. We find that, if after 15 years T2K and NOvA have not observed a 90% CL hint of CP violation, then LBNE and T2HK have less than a 10% chance of achieving a 5sigma discovery, whereas NF10 still has a ca 40% chance to do so. Conversely, if T2K and NOvA have an early 90% CL hint in 5 years from now, T2HK has a rather large chance to achieve a 5sigma CP violation discovery (75% or 55%, depending on whether the mass hierarchy is known or not). This is to be compared with the 90% (30%) probability that NF10 (LBNE) would have to observe the same signal at 5sigma. A hierarchy measurement at 5sigma is achievable at both LBNE and NF10 with more than 90% probability, irrespectively of the outcome of T2K and NOvA. We also find that if LBNE or a similar very long baseline super-beam is the only next generation facility to be built, then it is very useful to continue running T2K and NOvA (or at least T2K) beyond their original schedule in order to increase the CP violation discovery chances, given their complementarity.

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arXiv2012

European Strategy for Accelerator-Based Neutrino Physics

Massive neutrinos reveal physics beyond the Standard Model, which could have deep consequences for our understanding of the Universe. Their study should therefore receive the highest level of priority in the European Strategy. The discovery and study of leptonic CP violation and precision studies of the transitions between neutrino flavours require high intensity, high precision, long baseline accelerator neutrino experiments. The community of European neutrino physicists involved in oscillation experiments is strong enough to support a major neutrino long baseline project in Europe, and has an ambitious, competitive and coherent vision to propose. Following the 2006 European Strategy for Particle Physics (ESPP) recommendations, two complementary design studies have been carried out: LAGUNA/LBNO, focused on deep underground detector sites, and EUROnu, focused on high intensity neutrino facilities. LAGUNA LBNO recommends, as first step, a conventional neutrino beam CN2PY from a CERN SPS North Area Neutrino Facility (NANF) aimed at the Pyhasalmi mine in Finland. A sterile neutrino search experiment which could also be situated in the CERN north area has been proposed (ICARUS-NESSIE) using a two detector set-up, allowing a definitive answer to the 20 year old question open by the LSND experiment. EUROnu concluded that a 10 GeV Neutrino Factory, aimed at a magnetized neutrino detector situated, also, at a baseline of around 2200 km (+-30%), would constitute the ultimate neutrino facility; it recommends that the next 5 years be devoted to the R&D, preparatory experiments and implementation study, in view of a proposal before the next ESPP update. The coherence and quality of this program calls for the continuation of neutrino beams at CERN after the CNGS, and for a high priority support from CERN and the member states to the experiments and R&D program.

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